1. Field of the Invention
This invention relates to digital video systems, more particularly to the display of motion video sequences on digital display systems.
2. Background of the Invention
As television moves from an analog system to a digital system, several problems arise. One such problem occurs in the depiction of moving objects across the field of display.
When an object moves across the display in an analog system, the edges, or the object boundaries, remain true to life, with no real difficulties in portraying curves, diagonals and other features of the objects in motion. One example of an edge would be the curve of a red ball against a blue background. However, in a pixelated display with individual cells instead of lines of continuous images, the edge integrity becomes harder to maintain.
An additional problem is that most conventional televisions use an interlaced format, where the display device draws every other line during one interval, then draws the missing lines in the second interval. In a digital television using such techniques as progressive scan, where every line is "drawn" during the same interval, the missing data from the second interval must be interpolated. Interpolation of moving objects creates artifacts, or visual images that have errors in them.
Rounded edges on an object such as a ball present no real problems when stationary. The curves smooth out through the use of prior field data of the stationary object. Without the use of prior field data, a curve would have a jagged edge, looking much like a stair step or serrated edge. When the object moves, however, previous field data can no longer be used due to the lack of correlation between the present field and the past field. Hence, line averaging techniques using the current field are often employed for the interpolation process. Simple line averaging techniques suffer from a lack of perceived resolution which is evidenced by blurring and serrated edges. These visual artifacts are due to an interpolation process that does not take into consideration the actual edge content of the data.
The adaptive techniques used have been unsatisfactory in resolving moving edges. The resulting picture has artifacts such as the serrated edges mentioned above, that detract from the advantages of high-definition television (HDTV) or the generally sharper picture possible in digital televisions.
Some method is needed that allows the display to portray moving edges in keeping with the clarity and sharpness available in digital television, that also is usable in the higher speed environment of progressive scan without a huge increase in the processing requirements.